Dry pumps

ABSTRACT

A dry pump apparatus comprises; a pumping mechanism, a controller for controlling the operation of the pumping mechanism, and a sensor for sensing the operating temperature of the pumping mechanism. The controller is configured to carry out an automated shutdown sequence involving the following steps; a) ceasing operation of the pumping mechanism b) monitoring the temperature of the pumping mechanism by means of the temperature sensor c) at least one pre-selected temperature interval, initiating operation of the pumping mechanism for a fixed time period so as to purge a proportion of contaminant particulate matter present until a predefined temperature is reached or a predefined time limit has passed. By carrying out these steps the incidence of powder compaction between component parts of the apparatus which may contract during shutdown, and consequential restart failure and down time, can be significantly reduced.

This invention relates to dry pumps and in particular to the clearing ofparticulate dirt from dry pumps.

Dry pumps typically comprise non-contacting, self-valving mechanisms andno oil or lubricants in the pumping mechanism. The component parts ofthese pumps are manufactured to tight tolerances to provide fixedrunning clearances between components and reduce friction or otherreactive forces, which may reduce the efficiency of the pump mechanism.The pumps are used in many manufacturing applications, one of the majorof which is semi-conductor manufacture. The pumps are used to providethe very clean, near vacuum environment needed for the manufacture ofquality semi-conductor products. The skilled addressee will no doubt befamiliar with other common applications of dry pump technology.

Many industries including the semi-conductor industry produceparticulate or powderous waste or bi-products which are withdrawn fromthe manufacturing environment by pumps such as the dry pumps to whichthis invention relates. In the semi-conductor industry it is usual formanufacturing lines to run twenty four hours a day, thus, dry pumps usedin this application are in continuous use except where there is a needfor a manufacturing line change or maintenance or repair of the pump.The pumps have an inlet purge function on shut down for evacuatingcontaminants from the pump mechanism, but these purge functions rarelyoperate one hundred per cent efficiently and some level of particulatecontamination invariably remains within the pump.

Running temperatures for dry pumps in semi-conductor manufacturing linesare typically around 120° C, when the pumps are switched off, they coolto normal room temperature (around 19° ), the components (such as rotorsand stators in the pump mechanism) contract, reducing the runningclearances between them and any particulate contaminants present in themechanism are compacted in between the contracted components. Onrestart, where the torque required to overcome the friction caused bythe presence of these particulate materials compacted between thecomponents is higher than the operational torque of the pump, start-upfailure occurs.

The present invention aims to maintain running clearances of dry pumpsand minimise the occurrence of restart failure due to compactedparticulate contaminants.

In accordance with a first aspect, the present invention provides a drypump apparatus comprising;

a pumping mechanism,

a controller for controlling the operation of the pumping mechanism, and

a sensor for sensing the operating temperature of the pumping mechanismwherein the controller is configured to carry out an automated shutdownsequence involving the following steps;

a) ceasing operation of the pumping mechanism

b) monitoring the temperature of the pumping mechanism by means of thetemperature sensor

c) at at least one pre-selected temperature interval, initiatingoperation of the pumping mechanism for a fixed time period so as topurge a proportion of contaminant particulate matter present until apredefined temperature is reached or a predefined time limit has passed.

This pulsed purging method effected by the controller of the dry pumpapparatus enables small amounts of contaminant to be evacuated from thepump as it cools so that when the apparatus is cooled to the ambienttemperature, there is significantly less particulate contaminant in thepumping mechanism than there would otherwise be. Thus, the particulatematerial is less compact and frictional forces to be over come onstart-up, significantly less. Consequently, the occurrence of failure onrestart is significantly reduced.

It will be understood that this pulsed shut down method is what providesthe technical improvement in the function of prior art dry pumps.Accordingly, in a second aspect, the invention provides a method forreducing the incidence of restart failure in a dry pump comprising thesteps of;

a) detecting the cessation of operation of the pumping mechanism

b) monitoring the temperature of the pumping mechanism after cessationof operation

c) at at least one pre-selected temperature interval, initiatingoperation of the pumping mechanism for a fixed time period so as topurge a proportion of contaminant particulate matter present until apredefined temperature is reached or a predefined time limit has passed.

The controller of the dry pump apparatus may comprise a microprocessorwhich may be embodied in a computer, which in turn is optionallyprogrammed by computer software which, when installed on the computer,causes it to perform the method steps a) to c) mentioned above.

In a third aspect therefore the invention comprises a program for acomputer which, when installed on the computer, causes it to perform themethod steps of;

a) detecting the cessation of operation of the pumping mechanism

b) monitoring the temperature of the pumping mechanism after cessationof operation

c) at at least one pre-selected temperature interval, initiatingoperation of the dry pump for a fixed time period so as to purge aproportion of contaminant particulate matter present until a predefinedtemperature is reached or a predefined time limit has passed.

In a fourth aspect, the invention comprises a computer readable carriermedium which carries a computer program which when installed on acomputer, causes it to perform the method steps of;

a) detecting the cessation of operation of the pumping mechanism

b) monitoring the temperature of the pumping mechanism after cessationof operation

c) at at least one pre-selected temperature interval, initiatingoperation of the dry pump for a fixed time period so as to purge aproportion of contaminant particulate matter present until a predefinedtemperature is reached or a predefined time limit has passed.

The carrier medium may be selected from but is not strictly limited to afloppy disk, a CD, a mini-disc or digital tape.

In one preferred option, the pulsed shut down method is performed atintervals corresponding to regular drops in the internal temperature ofthe pump apparatus. A suggested temperature drop interval is 10 degreesthough this is not essential. The interval may equally be 2 degrees, 30degrees or anything in between. Appropriate temperature intervals may beselected based on the cooling conditions, the amount of time availablefor the pulsed shut down process and other factors. Alternatively lessregular temperature intervals may be pre-selected. For example a numberof small intervals (eg 2 degrees) may be selected for the early part ofthe cooling period and increasingly larger intervals as the apparatusapproaches the predefined “cool” temperature.

The fixed time period of the pulse is again variable and will desirablybe selected based on cooling conditions or other practical factors. Afixed time period of between 15 and 45 seconds is suggested, and about30 seconds considered practical. The fixed time period may be the samefor each pre-selected temperature interval, or may be different. Forexample, the period may be of relatively longer duration at lowertemperatures.

The duration of the pulse may be dictated by the apparatus reaching apredefined “cool” temperature, such as the usual room temperature.Alternatively, the method may be performed for a fixed time periodirrespective of the cooling time. In the latter case a duration of about2 hours is suggested, but not essential.

At the end of each fixed time period of operation of the pump mechanisma separate inlet purge function may be effected by the controller.

In some embodiments, the controller may be configured to cease thepulsed shutdown method when the first of a predetermined temperature ora predefined time limit has been reached.

The dry pump apparatus may be of any known form but one preferred formis a dry pump which includes a claw type rotor. Dry pumps of this formare known in the prior art. Briefly, they include a pair of shafts eachcarrying a pair of claw shaped rotors which rotate in oppositedirections to trap and compress gas flowing along the axis of the shaftsbetween each claw pair. During each complete rotation of the shafts,first the inlet port of each claw pair is exposed then both the inletand outlet are isolated, finally the outlet is exposed allowing trappedgas to be expelled. In these arrangements, the controller controls therotation of the shafts.

Since many existing dry pump apparatus include a controller which runssoftware for operating the pump, the invention can conveniently beimplemented by uploading the computer program of the invention to theexisting controller. Thus the control can be configured on shutdownautomatically to perform the pulsed shut down method of the invention.

For the purposes of exemplification, some embodiments of the inventionwill now be described with reference to the following Figures in which:

FIG. 1 illustrates the problem of particulate contamination addressed bythe present invention

FIG. 2 illustrates how the present invention affects the processillustrated in FIG. 1

FIG. 3 illustrates the method of the invention in a time line format

FIG. 4 illustrates the method of the invention in graph form.

FIG. 1 shows schematically the pumping mechanism of a dry pump apparatus1 having a drive unit D driving a pair of shafts 1 a, 1 b each carryinga stator Sa, Sb and a rotor Ra, Rb. FIGS. 1(a), 1(b) and 1(c) show therelationship between a rotor R and a stator S of the pumping mechanism.FIG. 1(a) illustrates the arrangement between the rotor R and stator Sat normal running temperature of the pump. The running clearance betweenthe stator S and rotor R is shown as d₁. As shown in FIG. 1(b) as theapparatus cools, the running clearance d₂ is reduced due to contractionof the shaft carrying the stator S and rotor R. As shown in FIG. 1(c),powder P which may have accumulated on the surface of the stator S, canbecome compacted in the reduced clearance between the stator S and rotorR. This compaction results in a frictional force to be overcome by therotor R if it is to rotate on restart of the apparatus. If sufficienttorque is not provided to the rotor R to overcome this frictional force,then start up failure occurs.

FIG. 2 shows in sequential order (Figures (a) to (f)) a stator S androtor R cooling from running temperature (FIG. 2(a)) to gradually coolertemperatures (FIGS. 2(b)-2(f)). In each of FIGS. 2(a) to 2(e), it can beseen that there is a layer of settled powder P settled on the surface ofthe stator S. It will also be noted that the clearance between thestator S and rotor R gradually decrease as the temperature of theapparatus falls. Between FIGS. 2(b) and 2(c), 2(c) and 2(d) and 2(e) and2(f), the pump is briefly activated and a proportion of the powder P isevacuated. Thus when the final cooling temperature is reached (FIG.2(f)) the quantity of powder is minimal and insufficient to cause anygreat counter force against the torque of the rotor on restart. Thus theoccurrence of start-up failure on restart is reduced.

FIG. 3 shows a time line of the pulsed shut down method of theinvention. As can be seen, in tandem with the pulse sequence shown inthe top line, a booster associated with the pump may be configured torun for a brief period after initial shutdown to aid in removal of anypowderous contaminant within the pump mechanism to reduce the initialquantity which may settle on the stator while the pumping mechanism isinactive. As can be seen form the top line of the figure, aftershutdown, the pump remains active for around 30 seconds and then isdormant for a period (Delta T=10 deg) while the internal temperature ofthe mechanism, monitored by the controller falls to 10 degrees(centigrade) below the normal operating temperature. When the period iscomplete, the pump is activated for 30 seconds then again held dormantuntil a further fall of 10 degrees in the monitored temperature. Thecycle is repeated until either the monitored temperature is 40° C., orthe time elapsed since the start of the sequence is two hours.

FIG. 4 illustrates the method of FIG. 3 in graphical form. The verticalaxis corresponds to the monitored temperature of the pumping mechanism,the horizontal axis corresponds to the passage of time. The thick, blackcurved line shows the monitored temperature gradually falling. Thethinner, pulsed line shows active and dormant periods of the pumpingmechanism during the cooling process.

It is to be understood that the foregoing represents just a fewembodiments of the invention, others of which will no doubt occur to theskilled addressee without departing from the true scope of the inventionas defined by the claims appended hereto.

1. A dry pump apparatus comprising; a pumping mechanism, a controllerfor controlling the operation of the pumping mechanism, and a sensor forsensing the operating temperature of the pumping mechanism wherein thecontroller is configured to carry out an automated shutdown sequenceinvolving the following steps; a) ceasing operation of the pumpingmechanism b) monitoring the temperature of the pumping mechanism bymeans of the temperature sensor c) at at least one pre-selectedtemperature interval, initiating operation of the pumping mechanism fora fixed time period so as to purge a proportion of contaminantparticulate matter present until a predefined temperature is reached ora predefined time limit has passed.
 2. A dry pump apparatus as claimedin claim 1 wherein the controller comprises a microprocessor.
 3. A drypump apparatus as claimed in claim 2 wherein the microprocessor isembodied in a computer.
 4. A dry pump as claimed in claim 3 wherein thecomputer has installed thereon computer software which causes it toperform the method steps a) to c).
 5. A dry pump apparatus as claimed inclaim 1 wherein the pumping mechanism includes a claw type rotorarrangement.
 6. A method for reducing the incidence of restart failurein a dry pump comprising the steps of; a) detecting the cessation ofoperation of the pumping mechanism b) monitoring the temperature of thepumping mechanism after cessation of operation c) at at least onepre-selected temperature interval, initiating operation of the pumpingmechanism for a fixed time period so as to purge a proportion ofcontaminant particulate matter present until a predefined temperature isreached or a predefined time limit has passed.
 7. A method as claimed inclaim 6 wherein step c) is performed at preselected temperatureintervals corresponding to regular drops in the monitored temperature ofthe pumping mechanism.
 8. A method as claimed in claim 7 wherein theregular drop interval is 10° C.
 9. A method as claimed in claim 6wherein the fixed time period is between 15 and 45 seconds inclusive.10. A method as claimed in claim 6 wherein the fixed time period is thesame for each pre-selected temperature interval.
 11. A method as claimedin claim 10 wherein the fixed time period is 30 seconds.
 12. A method asclaimed in claim 6 wherein the fixed time period is different for eachpre-selected temperature interval.
 13. A method as claimed in claim 6wherein the method is performed for a predefined time limit.
 14. Amethod as claimed in claim 13 wherein the predefined time limit is 2hours from cessation of operation.
 15. A method as claimed in claim 6wherein at the end of each fixed time period of operation of the pumpmechanism a separate inlet purge function is effected by the controller.16. A method as claimed in claim 6 wherein the method is ceased when thefirst of a predetermined temperature or a predefined time limit has beenreached.
 17. (canceled)
 18. A computer readable carrier medium whichcarries instructions adapted to be executed by a processor, theinstructions which, when executed, define a series of steps to carry outan automated shutdown sequence of a dry pumping mechanism, comprising:a) detecting the cessation of operation of the pumping mechanism; b)monitoring the temperature of the pumping mechanism after cessation ofoperation; and c) at at least one pre-selected temperature interval,initiating operation of the pumping mechanism for a fixed time period soas to purge a proportion of contaminant particulate matter present untila predefined temperature is reached or a predefined time limit haspassed.
 19. The computer readable carrier medium as claimed in claim 18wherein the medium is selected from; a floppy disk, a CD, a mini-disc ordigital tape. 20-22. (canceled)
 23. The computer readable carrier mediumas claimed in claim 18 wherein at the end of each fixed time period ofoperation of the pump mechanism, a separate inlet purge function iseffected by the controller.
 24. The computer readable carrier medium asclaimed in claim 18 wherein step c) is performed at pre-selectedtemperature intervals corresponding to regular drops in the monitoredtemperature of the pumping mechanism.